A Scleral Lens Sensor to Assess the Severity of Dry Eye Disease
By Melissa Barnett, OD
A variety of tools are used to diagnose dry eyes. Patient symptoms, examination of the ocular surface, and symptom questionnaires are the most common approaches for diagnosis. Additional methods include Schirmer’s testing to measure tear fluid volume, fluorescein and lissamine staining to determine damage of the cornea and conjunctiva, and tear breakup time testing to evaluate tear evaporation. While each of these tests provides some information, they are all insufficient to identify the underlying causes of dry eye.
Additional tests provide supplementary information, yet they still have limitations. Osmometers measure tear hyperosmolarity, and lateral-flow assays test matrix metalloproteinase-9 levels or determine lactoferrin and IgE levels. There is no single test that can provide a comprehensive classification for dry eye; this may be due to varying etiological causes of dry eye.
According to the Tear Film & Ocular Surface Society’s Dry Eye Workshop II (TFOS DEWS II) definition and classification report, dry eye is a multi–factorial disease of the ocular surface.1 It is important to differentiate between aqueous deficient and evaporative dry eye, which occur as a continuum; this aids practitioners in the diagnosis and management of dry eye. Quantitative analysis of electrolyte composition in tear analytes using point-of-care testing can provide early diagnosis and novel personalized management strategies for dry eye disease.
A recent study used a fluorescent scleral lens sensor to quantitatively measure physiological levels of pH, sodium ions (Na+), potassium ions (K+), calcium ions (Ca2+), magnesium ions (Mg2+), and zinc ions (Zn2+).2 A variety of probes for pH and for each ion are highly selective and sensitive. In the study, the fluorescent sensors were then multiplexed in the concavities of an engraved scleral lens made of paflufocon. A carbon dioxide (CO2) laser was used to create microconcavities in a scleral lens. These microconcavities were oxygen-plasma-treated through a mask cut from a soft contact lens. To enclose the microchannels, the scleral lens sensors were sealed with silicone hydrogel. The scleral sensor is both excited and can be read by a handheld ophthalmic readout device composed of light-emitting diodes and bandpass filters. Basically, it quantitatively measures the fluorescence emission of pH and electrolytes to assess the tear film in a point‐of‐care setting, which allows practitioners to differentiate between the dry eye subtypes. A smartphone camera app and user interface provide quantitative measurements and data deconvolution, which recreates the signal as it existed prior to convolution (i.e., the impulse or frequency response). The future will tell how a scleral lens sensor point-of-care test will perform in clinical practice to diagnose and manage dry eye disease.
Craig JP, Nichols KK, Akpek EK, et al. TFOS DEWS II Definition and Classification Report. Ocul Surf. 2017 Jul;15:276-283.
Yetisen AK, Jiang N, Castaneda Gonzalez CM, et al. Scleral Lens Sensor for Ocular Electrolyte Analysis. Adv Mater. 2019 Dec 13:e1906762. [Epub ahead of print]
Dr. Barnett is a principal optometrist at the University of California Davis Eye Center in Sacramento, specializing in anterior segment disease and specialty contact lenses. She is the past president of the Scleral Lens Education Society. She is an advisor to and/or has received honoraria or travel expenses from AccuLens, Alcon, Alden Optical, Allergan, Bausch + Lomb, Bruder, Contamac, CooperVision, EveryDay Contacts, Johnson & Johnson Vision, Ocusoft, Paragon Bioteck, RaayonNova, ScienceBased Health, Shire, SynergEyes, and Visioneering Technologies.